Dr. Oliver Sacks is probably best known as the real inspiration for the caring neurologist portrayed by Robin Williams in the Oscar-nominated film, Awakenings, which was based on his autobiographical book. That film told the story of his work with patients with Parkinson’s disease and the double-edged sword of a drug that gave some of them the ability to move and speak after years of paralysis or involuntary movements, but also caused terrible side effects for many. Now the bestselling author has brought his coruscating mind to Hallucinations, his latest book exploring what happens when we see, hear, feel or smell things that aren’t there.

Do you think everybody hallucinates at some point?

I suspect so. Every so often, I give a class with students from Columbia [University] or New York University; if I speak on the matter, especially if it’s a small class and they all get comfortable, after an hour or two it starts to come out that everyone has a few experiences.

What is the most common form of hallucination?

Hearing one’s name is a pretty common one. And in our society, hearing the phone or feeling it. But I think a hallucination of patterns and geometrical patterns is [also] pretty common. Lots of people have it when they close their eyes right before they sleep at night. You can have it in a migraine. And it’s often a starting point with various drugs taken deliberately or accidentally, therapeutically or recreationally.

Geometric hallucinations tend to look like things made by people, like oriental rugs or designs seen in buildings with right angles and straight lines—not things you would see, say, in a forest or in nature…

I think the brain will utilize angles and patterns to decipher a natural scene and has a sort of lexicon of these forms. The geometrical things are sort of simpler. They’re symmetrical, they’re repetitive and sometimes are funnel-shaped or whatever. But these seem to be patterns which are inherent in the occipital lobes, in the primary visual cortex. So you’re seeing your own brain at work.

So you’re getting the lower levels of processing that normally get censored.

Yes. The lowest levels, which have nothing to do with memory or personality or situation. It’s almost as if the brain is idling. At various levels of hallucination, you have the appearance of things which are normally sort of embedded. But they can be very, very novel and one can hallucinate colors and smells one has never experienced and never imagined.

Is there an auditory equivalent of the sort of lower-level processing?

Yes. Noises, hisses, rumblings, twitches, jitters, which are not music and not speech.

What do you think distinguishes the people who hear voices and are schizophrenic and the ones who just hear voices and simply think, ‘Okay, I hear voices.’

We don’t know. We know relatively much more about visual hallucinations. But the non-schizophrenic voices heard are often commonplace. I mean I gave a personal example of when I took Artane, which is a deliriant. I was waiting for all sorts of exciting things to happen. While I was waiting for something to happen, in fact it was happening, but I wasn’t aware of it, which was my friends had come in and I was chatting to them and saying, ‘How do you like your ham and eggs?’ I heard their voices there, but it was not like a schizophrenic [hallucination].

What is the cause of Charles Bonnet syndrome, where people start to see things like little gnomes or Kermit the frog, but they don’t have any psychiatric problems?

It depends, but not exclusively, on impairment of vision and visual input. It’s as if the visual plane has to be active. It’s active in perception, dreaming, imagination. All of these things sort of hold it together but perception is the main constraint.

This is supported by the fact that if one is blindfolded, within two or three days, most people start to get visual hallucinations. It’s obviously not the whole story because if 20 percent of the visually impaired get complex hallucinations, 80 percent don’t. Although, it does seem that something like 80 percent get the geometrical hallucinations. I’m one of those 80 percent.

So do you see them now?

Yeah. I need to look at a blank surface now. I’m seeing them all over the ceiling. They mostly take letter-like forms. They look like Ms and Ns and Vs and they rapidly shift and they form all over. Sometimes, if I look at a horizontal like that, they will organize themselves into a sort of frieze. At the moment they are really colorless, but I tend to get blue and orange.

You write also about the grief hallucinations that some people have, where they see a loved one: in contrast, that may be very comforting.

Yes. In general, hallucinations have a bad name. He’s gone mad, he’s losing his mind, he’s getting demented. People have this feeling very strongly. In particular, hearing voices gets equated with schizophrenia, mental illness. One of the reasons I’ve put the book together is to say, ‘This isn’t necessarily so.’ There are all sorts of hallucinations, which don’t have an ominous significance.

We have this somewhat artificial distinction between neurological and psychiatric problems, even though both must involve something going wrong in the brain. With psychiatric illnesses, we don’t know what it is but with neurological problems, you can often see a lesion. Is there anything else that distinguishes those two categories, particularly in terms of hallucinations?

In general, psychotic hallucinations, whether they’re auditory or visual have meaning [for the person]. They mirror one’s fears, wishes, fantasies, conflicts, complexes, whatever. They’re projections for these and there’s usually a sense of an agent who is putting thoughts into one’s mind or whose voices one hears. This is, I think, in all psychoses almost a way of defining them, not just schizophrenic ones.

[But psychotic] hallucinations are only a very small category of hallucinations, a hundredth of one percent or something like that. On the whole, hallucinations [from neurological disorders] are not felt as having much personal relevance.

So the schizophrenic hallucinations are closer to the self and the neurological ones, with some exceptions are typically not…

Hallucinations are a nice mixture of ‘I’ and ‘it.’ They’re like isolated modules, sensory parts of the brain. But the self on the whole is not strongly involved in these sort of hallucinations, with some exceptions. The epileptic, the so-called ecstatic seizures are one. In [these], people imagine, feel, know that they are in heaven, that God is speaking with them or whatever.

Why do you think people are attracted to hallucinogenic drugs?

Well, we’re curious, we’re told stories, some of us sometimes want a different sort of experience, a different sort of consciousness, even if it doesn’t involve hallucination, even if it does make us see the colors brighter and the food tastier or gives one a good feeling and a bit of euphoria. It doesn’t have to be something sort of transcendent.

Seeing things that aren’t there and having a chemical completely shift your consciousness can enable empathy, because you realize that your point of view— whether you are high or not— is limited and subjective.

Certainly at some level, I think my own drug taking opened me to descriptions by my patients of some of their experiences. And to take a very simple thing, sometimes with acid [LSD] for me the sense of visual motion would disappear and I would see a series of stills as if a strobe light was flashing. But I’ve heard exactly this sort of description from some of my Parkinson’s patients and some migraine patients. You can say, ‘I understand’ or ‘Tell me more,’ instead of dismissing it or ignoring it or saying that’s impossible.